Ammonium nitrate base blasting agent



Sept. 4, 1962 C. O. DAVIS ET AL AMMONIUM NITRATE BASE BLASTING AGENTFiled June 14, 1961 EFFECT OF WATER N WEIGHT 0F ANHDNIUH NITRATE PERUNIT VOLUME POUNDS 0F AMHONTUH NITRATE PER CUBIC FOOT l0 I5 I WATER(BASED ON TOTAL WEIGHT 0F BLEND) I INVENTORS CLYDE OLIVER DAVIS HARTWELLHENRY FASSNACHT WILLIAM EARLE KIRST CHARLES HARDING NOREN BY 3 a gATTORNEY rates atent ire AlVflVlONIUM NITRATE BASE BLASTING AGENT ClydeOliver Davis and Hartwell Henry Fassnacht, Wenonah, and William EarleKirst, Woodbury, 'N.J., and Charles Harding Noren, Aurora, Col0.,assignors to E. I. du Pout de Nemours and Company, Wilmington, Del., acorporation of Delaware Filed June 14, 1961, Ser. No. 116,984 5 Claims.(Cl. 149-60) The present invention relates to a novel blasting agent.More particularly, this invention relates to a blasting agent especiallyadapted for use in large-scale blasting operations, such as quarrying,open-pit mining, and stripping operations. This application is acontinuation-in-part of our copending application Serial No. 644,595,filed March 7, 1957, now abandoned.

The main function of an explosive charge in a blasting operation is toprovide the energy needed to release material from its natural formationand, to the extent practicable, to render that material in a form inwhich it can be handled or processed further with minimum difficulty.The cost of the explosive and of preparing the site for the blastingoperation are basic to the ultimate cost of recovering the desiredmaterial in usable form. For the foregoing reason, much effort has beenexpended in the past to reduce the cost of the explosive and also toreduce the cost of preparing the site for blasting. The attainment ofboth goals has not always led in the same direction. For example, thecosts of preparing a site for blasting can be reduced if fewer boreholesare required per ton of material released. Because the energy requiredto release the material remains the same, fewer boreholes are practicalonly if the energy per borehole can be increased and if the material tobe blasted will break properly with wider hole spacings. One method ofaccomplishing such increased energy per borehole is by drilling largerboreholes. Within limits, some economy can be effected by suchprocedure, but the additional cost of drilling larger boreholes preventsunlimited extension of this technique. An alternative method involvesusing explosives of higher bulk strength. In the past, however, higherbulk strength has been obtainable only by using a larger percentage ofhigh explosive compounds, such as nitroglycerin and trinitrotoluene, inthe explosive composition. These ingredients are expensive tomanufacture, thus make the composition higher priced.

As a result of the foregoing, the industry has, to a large extent, hadto balance the various factors to achieve the maximum blastingefliciency. Therefore, in areas where large boreholes are lesspracticable, the explosives generally used are those containing highexplosive ingredients to provide the bulk strength required to give goodblasting results with a smaller volume of explosive per ton of materialreleased. In areas where larger boreholes are feasible, theless-sensitive and lower cost explosive compositions are used despitetheir lower bulk strength.

The compositions which have had the greatest adoption by the industrybecause of their relative insensitivity and their low cost arecompositions consisting primarily of ammonium nitrate in admixture witha combustible, nonexplosive fuel. When adequately primed and whenpresent in large diameter, i.e., in a cross-sectional area of at least 3square inches, such compositions can be detonated to produce the energyrequired to shatter and throw ore and rock. The bulk density of theammonium nitratefuel compositions ranges from about 0.8 to a maximum orabout 1.1 grams per cubic centimeter. Because such compositions haveessentially no water-resistance, they are generally packaged in rigid,water-impermeable containers, usually of metal or multi-ply paperboardheavily waxed or otherwise waterproofed. The quantity of this blastingagent which can be introduced into a borehole is thus limited to thevolume of the containers which can be introduced into the borehole. Totake advantage of the remaining space in the borehole, free-flowingpellets of a Water-resistant high explosive, i.e., TNT, are frequentlyintroduced into the borehole after the ammonium nitrate-fuel packageshave been loaded. The cost of the water-impervious container and of thehigh explosive pellets greatly increases the cost of the charge perborehole.

Recently the use of a flexible packaging material, e.g., polyethylene orpolyvinyl chloride film, for the ammonium nitrate-fuel mixture hasgained some acceptance in areas Where large boreholes are used and theholes are essentially dry. The flexible packaging material protects thecontents adequately from atmospheric moisture. When the composition thuspackaged is loaded into the borehole, the flexible material permits thecomposition to spread to fill substantially the borehole from side toside. However, these packages cannot be made as waterproof as rigidcontainers and do not have the resistance to tear or puncture needed foruse in boreholes containing moisture. Also, the density of thecomposition in the borehole is only about 0.8 gram per cubic centimeter.An alternative to the foregoing for dry boreholes involves dumpingprilled ammonium nitrate-fuel mixtures directly into the borehole.Again, this practice is being used only in dry boreholes and, again, thedensity of the composition in the borehole is only about 0.8 gram percubic centimeter. Thus, in either case, the bulk strength of the chargeis undesirably low.

Accordingly, an object of the present invention is to provide a blastingagent wherein low-cost ingredients are used, and wherein the foregoingdisadvantages are overcome. Other objects will become apparent as theinvention is more fully described.

We have found that the foregoing objects are achieved when we provide asa blasting agent an essentially uniform blend of solid ammonium nitrate,a fuel, and an aqueous solution of dissolved ammonium nitrate, the totalwater present being between 5 and 20% by weight based on said blend. Wehave further found that a highly effective blasting operation isattained when the described blasting agent is loaded in a borehole in amanner such that it substantially fills every portion of said boreholenot otherwise occupied by solid materials, and an adequate primer isimbedded in said blend to initiate the blend.

The present invention is based on the surprising discovery that,contrary to the well established belief in the industry, the presence ofa relatively large amount of water in an ammonium nitrate-fuel mixturewill not prevent propagation of explosion in a confined column of suchmixture provided that the water is present in the form of an aqueoussolution of ammonium nitrate, and the blend thus produced issubstantially uniform in composition throughout. The blasting agent ofthe present invention is advantageous, however, not because water may bepresent in an ammonium nitrate-fuel mixture, but because the effectiveblasting energy of an ammonium nitrate-fuel mixture can be increased bythe incorporation of an aqueous solution of ammonium nitrate, theammonium nitrate dissolved in said solution preferably constituting atleast 60% by weight of said solution. The increased blasting energy isobtained because the quantity of the energy-producing ammoniumnitrate-fuel mixture per unit volume is increased when a portion of theammonium nitrate is in the form of an aqueous solution. In any suchblend, the aqueous solution will be saturated; the quantity of ammoniumnitrate in the solution will depend on the temperature and the quantityof other water-soluble ingredients present. At a temperature of 50 F., atemperature slightly below the average temperature within a borehole,the ammonium nitrate in a saturated aqueous solution will constituteapproximately 62% by weight of the solution. At average summertimeatmospheric temperatures, i.e., about 70 F., the ammonium nitrate willconstitute about 66% by weight of a saturated aqueous solution. When anaqueous solution of ammonium nitrate is blended with solid ammoniumnitrate, either in the presence of a fuel or without, the aqueoussaturated solution occupies the voids between the granules of the solidammonium nitrate, thereby increasing by the amount of ammonium nitratein the solution the total amount of ammonium nitrate per unit volume.

In order to illustrate the foregoing, reference is now made to theaccompanying drawing which shows graphically the effect of water on theweight of ammonium nitrate per unit volume. The data was obtained bypreparing the different ammonium nitrate-saturated aqueous ammoniumnitrate blends and then determining the weight of each blend which wouldfill a specific volume. As shown on the graph, the number of pounds ofammonium nitrate per cubic foot of space rises from about 63.1 when nowater is present to about 81 when 10% water is presentan increase of 28%in the amount of ammonium nitrate which can be thus incorporated in aborehole. The graph shows that the beneficial effect of the increasedquantity of ammonium nitrate per unit volume is obtained over the rangeto 20% by weight of water with the maximum at about In order to furtherdescribe the present invention, reference is now made to the followingexamples. To demonstate the efficiency of various embodiments of thepresent blasting agent, a number of boreholes 2 /2 inches in diameterand from 40 to 45 inches in depth were drilled at a downward angle ofabout 45 in the face of a granite formation. The top of the borehole waslocated about 3 feet above the floor of the test area so that the bottomof the borehole was at approximately floor level. For each test, aprimer pellet of a 95/5 RDX/wax composition 2 inches in diameter by 3inches in length (200 grams) having a central cap-well containing a No.6 electric blasting cap was inserted to the bottom of the borehole, andthe described composition was then poured or tamped into the borehole.Velocity measurements by conventional means Were made to determine thepropagation of explosion by the blasting agent. In the examples, allproportions given are by weight, and all blends were prepared at 70 F.

Example I A blend of 80% ammonium nitrate, saturated aqueous solution ofammonium nitrate and 5% petroleum oil (containing a small quantity of anemulsifier-triethanolamine to facilitate blending) was tamped into theborehole. The density of the blend in the borehole was about 1.34 gramsper cubic centimeter and the water represented about 5% of the totalblend. Upon initiation of the primer, the blend detonated at a velocityof 1980 meters per second and produced a large crater 3 feet high, 5feet wide, and 37 inches deep in the granite formation.

Example II A blend of 56% ammonium nitrate, 31.5% saturated aqueousammonium nitrate solution, and 12.5% sugar was poured into a borehole.The blend had a smooth, creamy consistency and flowed very freely. Theamount of water was 10.5% based on the blend, and the density of theblend in the borehole was 1.54 grams per cubic centimeter. Uponinitiation, the blend detonated at a velocity of 1740 meters per secondand produced a crater 3 feet high, 5 feet wide, and inches deep.

Example III A blend of 47.5% ammonium nitrate, 47.5 saturated aqueousammonium nitrate solution, and 5% motor oil (containing a small quantityof an emulsifiertriethanolamine) was poured into a borehole. The slurrypoured freely, but showed no signs of segregation of ingredients onstanding. The water constituted 15.6% of the blend and the density ofthe blend in the borehole was 1.42 grams per cubic centimeter. Uponinitiation, the blend detonated at a velocity of 3970 meters per secondand produced a crater 3 feet high, 5 feet wide and 33 inches deep.

Example IV A blend of 56% ammonium nitrate, 38% saturated aqueousammonium nitrate solution, 4.8% fuel oil, and 1.2% corn starch waspoured into a borehole. The blend was readily pourable and its densityin the borehole was about 1.35 grams per cubic centimeter. The waterconstituted 12.6% of the blend. Upon initiation, the blend detonated ata velocity of 3400 meters per second and produced a crater 3 feet high,5 feet wide, and 45 inches deep.

In another series of tests carried out as described for the previousexamples, except that the boreholes were drilled into the floor of thegraphite formation instead of the face, and were 2% inches in diameterand 30 inches in depth, the following results were obtained.

Example V A blend of 48% ammonium nitrate, 32% saturated aqueousammonium nitrate solution and 20% cornmeal was poured into the borehole.The proportion of water was 10.6% and the blend had a density of about1.45 grams per cubic centimeter. No velocity measurements were obtained,but a conical crater 3 /2 feet in diameter by 30 inches in depth wasproduced when the blend was initiated.

Example VI A standard amatol composition ammonium nitrate-20% T T) wasloaded into the borehole in lieu of the blend for comparative purposes.The borehole was loaded to the same depth as in Example V. Uponinitiation, a crater approximately equal to that described in Example Vwas produced. This composition is representative of the highexplosive-sensitized ammonium nitrate compositions which the presentblend can replace.

Example VII A blend of 37% ammonium nitrate, 40% saturated aqueousammonium nitrate solution, 8% of finely divided aluminum, and 2% of cornstarch was poured into a spiralwound paperboard tube one end beingclosed, having a diameter of 27 8 inches and a length of 12 inches, andcontaining a SO-gram primer pellet of a 5 RDX/Wax composition and a No.6 electric blasting cap. The density of the slurry was 1.35 grams percubic inch and the water content was 13% by weight of the total blend.The open end was capped and the cartridge thus produced was submerged inwater. Upon initiation of the primer, the slurry detonated at a velocityof 3850 meters per second.

As indicated in several of the foregoing examples, the blend can be madevery fiowable, either as a slurry or having a creamy consistency. Ablend having such characteristics can be loaded into a borehole with aminimum of difficulty. For example, the blend can be poured directlyinto the borehole, and, without any further tamping, will completelyfill all unoccupied portions of the borehole to the level desired.Alternatively, such slurry or cream can be pumped through tubing or pipefrom a mixing or conveying unit to the borehole. For example, truckshaving mixing means can be loaded with the components and driven to theblasting site, all mixing occurring enroute. Alternatively, the truckscan be loaded with a premixed blend prepared at a storage and mixingstation. Portable mixers at the blasting site can also be used. Further,in boreholes containing water, the blend may be poured or pumped througha pipe or tube leading to the bottom of the borehole. The blend, beingof much higher density than the water, will displace the water upwardand completely fill the borehole from side to side from the bottom up tothe desired level. The water on top will act as stemming or may bedisplaced by earth or rock stemming. Because of the high density, i.e.,at least 1.3 grams per cubic centimeter, of the blend, further entranceof water through the strata surrounding the borehole is retarded if notentirely halted. For further protection of the blend, the borehole maybe lined with a tubing of a flexible sheeting, such as polyethylene orpolyvinyl chloride.

It is, however, essential that the borehole be substantially free ofvoids in the portion containing the blend. Our findings have led us tobelieve that discontinuities of the blasting agent will result infailure of propagation of the explosion. The foregoing is supported bythe known (failures which have resulted when packaged compositions ofammonium nitrate-fuel have been exposed to water in a borehole, as forexample, through leakage of the container. In such cases, the dissolvingof a portion of the ammonium nitrate would cause a decrease in the bulkof the contents in the container, thus producing a discontinuity ofblasting agent between adjacent containers. A layer of water betweenunits of relatively insensitive compositions will effectively haltpropagation of explosion in cases where propagation of explosion willinvariably be continued as an uninterrupted column or mass. Further, thepresence of voids, such as surround rigid explosive packages in aborehole because of the irregularities and larger diameter of theborehole, provides channels for the rapid escape of gases under pressurefrom the reaction zone. Inasmuch as the reaction of ammonium nitrate anda fuel is known to be pressure dependent, failure to maintain therequired high pressure at the reaction zone will cause the reactioninduced by the detonation of the primer to slow and finally stop longbefore much of the mass of the ammonium nitratefuel has begun reacting.To some degree, the foregoing difficulty can be overcome by using acontinuous primer, for example as a core surrounded by a sensitizedammonium nitrate composition. The provision of such continuous core ofprimer composition obviously greatly increases the quantity of highcost, highly sensitive explosive required, increases the loadingproblems, and, requires that the entire unit be treated as a highexplosive unit.

We have found that a primer of about 200 grams of high explosive isadequate to initiate the present blend when the blend is confined in aborehole and is free of discontinuities. The same primer will notinitiate the blend when the blend is packaged in a container of evenlarger diameter outside the borehole, even when under water confinement.Thus the safety inherent with the present blasting agent is apparent.For insurance against failure due to ground shift from previous blastsor defective initiation, the customary blasting practice of includingmore than the minimum required primer in the borehole will preferablyalso be followed in the use of the present blend. The usual practice isto locate primers every 20 or 30 feet along the borehole, all primersbeng initiated in sequence, for example, by a line of detonating fuse.

Therefore, included in the concept of this invention is a method ofblasting which comprises providing at least one primer and initiationmeans in a borehole, and providing as the main charge in said borehole ablend of ammonium nitrate, an aqueuos solution of ammonium nitrate, theammonum nitrate content of said solution preferably being at least 60%by weight, and a (fuel, the total amount of water being from to 20% byweight based on the weight of the blend, and the composition of theblend being uniform throughout its mass and hav- 6 ing a density of atleast 1.3 grams per cubic centimeter, wherein the portion of theborehole containing the said blend is essentially free of voids.

Throughout this description, the term fuel has been used to refer to anon-explosive combustible material which will react with ammoniumnitrate to form oxidized products. Preferably, the oxidized productswill be gases, such as are obtained from the combustion of carbonaceousmaterials, e.g., hydrocarbons, carbohydrates, urea, etc. However, theuse of fuels which produce nongaseous products, such as powdered metalsand alloys, e.g., aluminum, magnesium, iron, ferrosilicon, and the like,is also within the scope of this invention as is shown by Example VII.In summary, any of the non-explosive combustible materials used by theart as fuels in ammonium nitrate explosive compositions are included.The proportion of fuel required will vary according to its oxygenrequirements for complete oxidation. Generally, an oxygen-balanced blendis preferred, i.e., the proportion-s of fuel and inorganic nitrate aresuch that all the fuel will be converted to fully oxidized products bythe complete reduction of the oxidizing salt to stable products. Blendshaving an oxygen balance between +10 and 10% are acceptable. The fuelmay be either liquid or solid. For flowable compositions, liquid fuelsare preferred because they contribute to the mobility of the blend. Thefuel may be either water soluble, water absorbent, or Water insoluble.When a water-soluble fuel, such as sugar, is used, concentration of theammonium nitrate in the aqueous solution will be reduced somewhat,depending on the relative solubilities of the components and theirproportions in the blend. However, for effective blasting energy, theconcentration of the ammonium nitrate in the aqueous phase preferablywill be at least 60% by weight. As shown by the examples, the ammoniumnitrate concentration generally will be considerably higher. Withwater-insoluble fuels, the addition of a small quantity of anemulsifying agent is desirable to aid in the dispersal of the fuelthroughout the blend. The choice of emulsifier is dependent entirely onthe fuel and the economics involved, and is not critical to the presentinvention.

The use of other inorganic nitrates in conjunction with ammonium nitrateas the oxidizing salt is within the scope of this invention. As iscommonly known in the industry, replacement of up to 30% of the ammoniumnitrate by sodium nitrate, potassium nitrate, barium nitrate, etc., isfrequently desirable to modify the biasing action. Such modificationsare apparent to those skilled in the art and are not departures from thespirit of this invention. Accordingly, we intend to be limited only bythe following claims.

We claim:

1. A blasting agent consisting essentially of a uni-form blend of solidammonium nitrate, from about 5 to about 20% by weight of a non-explosivecombustible fuel selected from the group consisting of liquidhydrocarbons, carbohydrates and urea, and a saturated aqueous solutionof ammonium nitrate, the total water in said blend representing from 5to 20% by weight of said blend and the ammonium nitrate in the blendrepresenting at least 60% by weight of the blend, said blend having adensity of at least about 1.3 grams per cubic centimeter and the weightratio of ammonium nitrate to fuel in said blend being such as to providean oxygen balance of between +10 and 10%.

2. The blasting agent of claim 1 wherein said fuel is a liquidhydrocarbon fuel.

3. The blasting agent of claim 1 wherein said fuel is sugar.

4. The blasting agent of claim 1 wherein said fuel is a carbohydrate.

5. The blasting agent of claim 2 wherein said fuel is a liquid petroleumoil.

No references cited.

1. A BLASTING AGENT CONSISTING ESSENTIALLY OF A UNIFORM BLEND OF SOLIDAMMONIUM NITRATE, FROM ABOUT 5 TO ABOUT 20% BY WEIGHT OF A NON-EXPLOSIVECOMBUSTIBLE FUEL SELECTED FROM THE GROUP CONSISTING OF LIQUIDHYDROCARBONS, CARBOHYDRATES AND UREA, AND A SATURATED AQUEOUS SOLUTIONOF AMMONIUM NITRATE, THE TOTAL WATER IN SAID BLEND REPRESENTING FROM 5TO 20% BY WEIGHT OF SAID BLEND AND THE AMMONIUM NITRATE IN THE BLENDREPRESENTING AT LEAST 60% BY WEIGHT OF THE BLEND, SAID BLEND HAVING ADENSITY OF AT LEAST ABOUT 1.3 GRAMS PER CUBIC CENTIMETER AND THE WEIGHTRATIO OF AMMONIUM NITRATE TO FUEL IN SAID BLEND BEING SUCH AS TO PROVIDEAN OXYGEN BALANCE OF BETWEEN +10 AND -10%.